Communication among immunocompetent cells is crucially required for immunologic hemostasis. Existing among normal human T cells is a population whose communication with autologous B cells and monocytes (M0) can be depicted by their proliferation. Utilizing monoclonal antibodies, it has been possible to demonstrate that these autologous reactive T cells are actually heterogenous. One population is activated by signals derived from M0 and is required for help in immunoglobulin synthesis. The other responds to B derived signals and can suppress immunoglobulin production.